Re: [RFC 0/5] parker: PARtitioned KERnel

[Fam Zheng]

On Wed, Sep 24, 2025 at 9:10 PM Fam Zheng <fam@xxxxxxxxxx> wrote:
>
>
>
> On Wed, Sep 24, 2025 at 8:02 PM H. Peter Anvin <hpa@xxxxxxxxx> wrote:
>>
>> On September 24, 2025 8:22:54 AM PDT, Dave Hansen <dave.hansen@xxxxxxxxx> wrote:
>> >On 9/23/25 08:31, Fam Zheng wrote:
>> >> In terms of fault isolation or security, all kernel instances share
>> >> the same domain, as there is no supervising mechanism. A kernel bug
>> >> in any partition can cause problems for the whole physical machine.
>> >> This is a tradeoff for low-overhead / low-complexity, but hope in
>> >> the future we can take advantage of some hardware mechanism to
>> >> introduce some isolation.
>> >I just don't think this is approach is viable. The buck needs to stop
>> >_somewhere_. You can't just have a bunch of different kernels, with
>> >nothing in charge of the system as a whole.
>> >
>> >Just think of bus locks. They affect the whole system. What if one
>> >kernel turns off split lock detection? Or has a different rate limit
>> >than the others? What if one kernel is a big fan of WBINVD? How about
>> >when they use resctrl to partition an L3 cache? How about microcode updates?
>> >
>> >I'd just guess that there are a few hundred problems like that. Maybe more.
>> >
>> >I'm not saying this won't be useful for a handful of folks in a tightly
>> >controlled environment. But I just don't think it has a place in
>> >mainline where it needs to work for everyone.
>>
>> Again, this comes down to why a partitioning top level hypervisor is The Right Thing[TM].
>>
>> IBM mainframes are, again, the archetype here, having done it standard since VM/370 in 1972. This was running on machines with a *maximum* of 4 MB memory.
>>
>> This approach works.
>>
>> Nearly every OS on these machines tend to run under a *second* level hypervisor, although that isn't required.
>
>
I'm trying to think about the hypervisor approach you mentioned, but
if it doesn't provide memory and I/O isolation, what is the advantage
over this RFC? (if it doesn I think then we're talking about a
specially configured KVM which does 1:1 vcpu pinning etc).


Sorry, forgot to turn off email html mode in my previous message..


Fam